Mars Putting On A Show In Close Approach To Earth

Tonight, low in the southern sky near the teapot-shaped constellation Sagittarius, the bright ochre jewel of Mars will be just 37.5 million miles from Earth, the planet's closest approach since 1971.

The reason is that Mars will be in what astronomers call ''opposition,'' with the sun, Earth and Mars in a straight line in that order. Astronomers are excited because oppositions are the best times for viewing the planet involved.

Mars goes into opposition with the Earth every 26 months or so, but because of the eccentricity of the Martian orbit, the distance between the two planets can vary widely from one opposition to another. At the opposition of 1978, for example, Mars was a disappointingly featureless blob nearly 61 million miles away.

Tonight's opposition is special because Mars also happens to be nearing its closest approach to the sun, a point called perihelion. The result is a relatively rare perihelic opposition that usually occurs at intervals of 15 and 17 years.